The present invention relates to polymer nano-particles, a method for their preparation, and their use.
Polymer nano-particles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonic crystals. Similarly, vinyl aromatic (e.g. polystyrene) nano-particles have been prepared for uses as a reference standard in the calibration of various instruments, particularly in medical research and diagnostic tests. Such polystyrene nano-particles have been prepared by emulsion polymerization.
Nano-particles can be discrete particles uniformly dispersed throughout a host composition. Nano-particles preferably are monodisperse in size and uniform in shape. However, controlling the size of nano-particles during polymerization and/or the surface characteristics of such nano-particles can be difficult. Moreover, achieving better control over the surface composition of such polymer nano-particles also is desirable.
Rubbers may be modified by the addition of various polymer compositions. Such polymeric additives often improve the physical properties of rubber compositions. Specifically, moldability and tenacity are often improved through such modifications.
Recently, there has been considerable interest in forming nanocomposites as a means to improve the mechanical properties of polymers. Incorporating clay minerals in a polymer matrix, however, does not always result in markedly improved mechanical properties of the polymer. This may be due to the lack of affinity between the layered silicate materials and the organic polymers. Thus it has been proposed to use ionic interactions as a means of incorporating clay minerals in a polymer. This type of approach, unfortunately, has limited usefulness. Indeed, a more direct, simple, and economic approach to preparing nanocomposites is highly desirable.
Development of nano-particles having a crystalline surface layer which would be applicable to a wide variety of rubbers and elastomers is desirable because discrete particles could be thermally stable and could disperse evenly throughout the matrix to provide a uniform composition. Also, the potential benefits of nano-particles are pervasive in technologies including information technology, medicine and health, material and manufacturing, aeronautics and space exploration, environmental and energy applications. However, past attempts to form such nano-particles have been largely unsuccessful.
In one embodiment of the present invention, a polymer nano-particle composition is provided. The composition includes polymer nano-particles having a poly(alkenylbenzene) core and a surface layer comprising a crystalline polyolefin. The nano-particles preferably have a mean average diameter of less than about 100 nm.
In another embodiment, a process for forming polymer nano-particles is provided. The process includes polymerizing alkenylbenzene monomer and diene monomer in a hydrocarbon solvent to form a diblock polymer. After the polymerization has begun, a polymerization mixture including micelles of the diblock polymer is formed, followed by addition of at least one crosslinking, agent to the polymerization mixture. This addition aids in the formation of crosslinked nano-particles having a poly(alkenylbenzene) core and a poly(conjugated diene) surface layer from said micelles. In a final step, the poly(conjugated diene) surface layer is hydrogenated to provide a polycrystalline surface layer.
In a third embodiment, a polymer nano-particle is provided. The nano-particle includes a polycrystalline outer surface and a vinyl-substituted aromatic hydrocarbon contributed unit core including a crosslinking agent. The nano-particles are preferably less than 100 nm in diameter and have a Mw between about 100,000 and 3,000,000.
In another embodiment, a rubber composition including a blend of rubber and a plurality of polycrystalline nano-particles is provided.
Herein throughout, unless specifically stated otherwise:
xe2x80x9cvinyl-substituted aromatic hydrocarbonxe2x80x9d and xe2x80x9calkenylbenzenexe2x80x9d are used interchangeably; and
xe2x80x9crubberxe2x80x9d refers to rubber compounds, including natural rubber, and synthetic elastomers including styrene-butadiene rubber, ethylene propylene rubber, etc., which are known in the art.